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Retention of Hydrogen Isotopes in Divertor Tiles Used in JT-60U

Y. Hirohata et al.

Fusion Science and Technology

Volume 48 / Number 1 / July 2005 / Pages 557-560

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Retention characteristics of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U were investigated by thermal desorption spectroscopy (TDS). The deuterium retained in the near surface of all graphite tiles was mostly replaced by hydrogen due to exposure to hydrogen plasma at the final stage operations, resulting in main deuterium retention in the deeper region. The dominant species desorbed from the divertor tiles were H2, HD, D2 and CH4. The smallest retention of hydrogen isotopes (H+D) was observed in the outer divertor tile which was eroded with maximum of 20 m depth. The amount of H+D retained in the inner divertor tiles covered by the re-deposited layers increased with the thickness of the re-deposited layers. Hydrogen isotopes concentration ((H+D)/C) in the re-deposited layers was ~0.02, which was much smaller than those observed in JET and other devices.